Kinetics and Mechanism of the Reactions Between Triphenylphosphine,Dialkyl Acetylenedicarboxilates and a NH-Acid,Pyrazole, by UV Spectrophotometry

Kinetic studies were made of the reactions between triphenylphosphine and dialkyl acetylenedicarboxylates in the presence of a NH-acid such as pyrazole. To determine the kinetic parameters of the reactions, the reaction progress was monitored by UV spectrophotometry. The second-order fits were automatically drawn and the values of the second-order rate constant (k ₂) were automatically calculated using standard equations. In the temperature range studied, the dependence of ln k ₂ on the reciprocal temperature was consistent with the Arrhenius equation. Furthermore, useful information was obtained from studies of the effect of solvent, structure of the reactants (different alkyl groups within the dialkyl acetylenedicarboxylates), and also the concentration of reactants on the rate of reaction. The mechanism was confirmed to involve a steady-state condition with the first step of the reaction being the rate-determining step.